Friday marks anniversary of great Pacific Coast quake, tsunami

By Scott Sistek, KOMO News

Published
8:21 am PST, Friday, January 26, 2018

Friday marks the 318-year anniversary of one of the greatest earthquakes on record along the Pacific Coast - the estimated 9.2 "Cascadia" quake that struck just off our coast on Jan. 26, 1700. To coincide with the anniversary, NOAA and the Pacific Tsunami Warning Center have released a computer model depiction of how the devastating ensuing tsunami raced across the Pacific Ocean.

The quake's date was discovered in the 1980s after sleuthing over what caused a sudden tsunami to strike Japan just before midnight on Jan. 27, 1700.

"Scientists and historians in Japan and the United States solved the mystery of what caused this 'orphan tsunami' through careful analysis of historical records in Japan, as well as oral histories of Native Americans, sediment deposits, and ghost forests of drowned trees in the Pacific Northwest of North America, a region also known as Cascadia," the National Weather Service wrote on the YouTube pageshowcasing the simulation.

"By comparing the tree rings of dead trees with those still living they could tell when the last of these great earthquakes struck the region. The trees all died in the winter of 1699-1700 when the coasts of northern California, Oregon, and Washington suddenly dropped 1-2 m (3-6 ft.), flooding them with seawater," the Weather Service continued. "That much motion over such a large area requires a very large earthquake to explain it perhaps as large as 9.2 magnitude, comparable to the Great Alaska Earthquake of 1964. Such an earthquake would have ruptured the earth along the entire length of the 1000 km (600 mi) -long fault of the Cascadia Subduction Zone and severe shaking could have lasted for 5 minutes or longer. Its tsunami would cross the Pacific Ocean and reach Japan in about 9 hours, so the earthquake must have occurred around 9 o'clock at night in Cascadia on January 26, 1700".

"We also know the fault is reloaded with strain and capable of producing another great earthquake today though it is probable that we have many decades with which to prepare for this inevitable earthquake," Bill Steele with the Pacific Northwest Seismic Network wrote in this story five years ago chronicling the great quake.